Does it melt? What is combustion, etc, etc.
It is pretty much impossible to melt wood. The reason is that as you start heading the wood up, its constituent building blocks tend to break up before the material can melt. This behavior is due to the fact that wood is made up of a strong network of cellulose fibers connected by a lignin mesh. You would need to add a lot of energy to allow the cellulose fibers to be able to easily slide past each other in order to create a molten state. On the other hand, there are plenty of other reactions that can kick in first as you transfer heat to the material.
If you have oxygen around you one key reactions is of course combustion. But even in the absence of oxygen there are plenty of reactions that will break up the material at the molecular level. The umbrella term for all of these messy reactions driven by heat is called pyrolysis.